SILUKIAN. 247 



The subdivisions recognized so far in the Monroe, with their faunal characteristics (deter- 

 mined by Grabau), are as follows: 



LOWER MONROE. 



For this stratigraphic unit the name Bass Islands series is proposed, from the group of 

 islands of that name in western Lake Erie. No other appropriate term seems to be available, 

 though characteristic exposures of all the divisions are not found in these islands. 



(a) Greenfield dolomite. — This term was proposed by Grabau in 1898, though previously used 

 in. a commercial sense, for the dolomite found about Greenfield, Highland County, Ohio, and 

 exposed again in the regions about BallviUe, in northern Ohio. The name is here accepted for 

 this division, which is characterized by Schuchertella Tiydraulica (Whitfield), HindeUa? whit- 

 fieMi Grabau, H.f rostralis Grabau, Leperditia, etc. The faunal zone may be called that of 

 ScTbUchertella Tiydraulica. The thickness is 100 feet or more and the formation is the lowest known 

 subdivision of the Monroe. 



(6) Tymqchtee shales and limestones. — This name was proposed in 1873 byN. H. Winchell for 

 the shales and thin-bedded calcUutytes of the Monroe (Waterlime) series exposed in the creek of 

 that name in Crawford Township, Wyandot County, Ohio. The thickness there is something 

 over 100 feet, but the relation to the overlyiag and underlying formation is unknown. Its 

 fauna hkewise is unknown, and the formation must be considered a tentative division of the 

 Lower Monroe. It is not impossible that it represents in part one or more members recognized 

 elsewhere. 



(c) Put-in Bay dolomites. — This name is proposed for the extensive fossiliferous series of 

 water lime exposed on Put-in Bay Island, one of the Bass Islands, and characterized by the 

 fauna comprising Spirifer oJiioensis Grabau, Goniophora dubia Hall, Eurypterus eriensis Whit- 

 field, and Leperditia. From the abundance of the pelecypod, the paleontologic zone may be 

 called that of GoniopTiora dubia. Something over 100 feet of strata is exposed on Put-in Bay 

 Island, where the higher beds are in contact with the succeeding zone. The formation is also 

 known from Marion County, Ohio. Its thickness is over 100 feet, but the base is unknown. 



(d) Raisin River dolomites. — This name is proposed for the highest division of the lower 

 Monroe exposed in Lucas and Wood counties, Ohio, and in Monroe County, Mich., especially along 

 the Raisin River. It is perhaps 200 feet thick and contains several oolite zones. Its known 

 fauna comprises nearly 20 species, of which the most significant are WJiitfieldella prosseri Grabau 

 and Pterinea lanii Grabau. These are restricted to this horizon, so far as known. Spirorbis 

 laxus and numerous minute gastropods, besides plant remains, further characterize this horizon. 

 From the abundance of the brachiopod mentioned, which is everywhere found and characteristic, 

 the faunal zone is designated as that of Whitfieldella prosseri. 



MIDDLE MONROE. 



This is represented in Michigan only by the Sylvania sandstone. This is believed to rep- 

 resent a long interval at the end of which a new series of faunae invaded this region upon 

 resubmergence. The thickness of the Sylvania seldom exceeds 150 feet.' 



UPPER MONROE. 



For this stratigraphic unit the group name Detroit River series is here proposed, from the 

 exposure of all its members along that stream. It comprises four subdivisions or faunal zones. 



(a) Flat Rock dolomites. — These are exposed at Flat Rock, on the Huron River, and are 

 also found in the lower part of the salt shaft at Oakwood, near Detroit. The fauna so far 

 obtained is meager, comprising only the corals Syringopora cooperi Grabau, S. cf. hisingeri 

 Billings, and Favosites cf. maximus Troost. The first mentioned seems to be characteristic 

 and restricted to it, and the zone is provisionally called the Syringopora cooperi zone. The 

 thickness of the formation varies from 40 to 150 feet or more. 



(b) Anderdon limestone. — This name, suggested by the Rev. Thomas Nattress, was adopted 

 by Sherzer and Grabau for the coral reef limestone exposed in the Anderdon quarry, Essex 

 County, Ontario, 2 miles from Amherstburg, Ontario, and in the salt shaft at Oakwood, Detroit. 



